Pellegrini takes his side to Cardiff today demanding more of the Bosnian bought from Wolfsburg for £27m two and a half years ago.
Pellegrini said: "Dzeko played well against Newcastle, but not very, very well because for all the things he did he must score. Then he will have played very well indeed. He had bad luck. Of course I have no doubt he will score goals. He has scored goals through his whole career.
"I spoke with him before I arrived here and told him that if he will stay here this year he must demonstrate the player that Manchester City bought two years ago."
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